Structural phase transition in surface layer of metals

Abstract

In the article a review of various phenomena on the surface of pure metals is given: the occurrence of the sur- face states of Tamm and Shockley; quantum size effects; electric double layer, the work function of electrons from a metal. According to modern concepts, the surface layer is a very thin phase that is in thermodynamic equilibrium with volume. A new model of the surface layer of metals has been proposed. The main attention is paid to the structural phase transition in the surface layer. This question is raised by us for the first time. In order to describe phase transitions in nanostructures, various models have been proposed, among which we can mention the Landau mean field method, in which the order parameter is used. We will use the Landau theory, replacing the temperature T with the coordinate h. It was experimentally shown that the heat capacity jumps ΔC_p = 0, d = 1.15 (J/mol•K). The molecular dynamics calculations for the heat capacity of gold with particle sizes from 1.5 to 5.5 nm showed that ΔC_p ≈ 1.65 (J/mol•K). This is close to our result, given the proximity of computer calculations. The lattice parameter of gold is a = 0.4 nm. So the d (I) layer contains about 3 monolayers of atoms of gold and d (II) — about 6 monolayers of gold.